Coprecipitation synthesis and thermal conductivity of La 2Zr 2O 7

Abstract

Lanthanum zirconate (La 2Zr 2O 7, LZ) was synthesized by a coprecipitation–calcination method with different dropping orders for the raw materials. We investigated synthesis procedures, including the chemical compositions of precipitate mixtures, the calcination process and the phase composition at different calcination temperatures. Simultaneous thermogravimetric and differential thermal analysis (TG–DTA) results of the mixtures show two different calcination processes for precipitates by the natural dropping and reverse dropping methods. Reactions starting in a basic solution (the reverse dropping method) can precipitate La and Zr ions simultaneously and form a –La–O–Zr– composite, resulting in a homogeneous composition on a molecular scale, and pure, high-crystalline LZ powders after calcination. When starting from an acid solution (the natural dropping method), the precipitate was a mixture of lanthanum hydroxide and zirconium hydroxide. Consequently, the final product was LZ with impurities. The overall thermal conductivity of LZ obtained by the reverse dropping method was about 50% lower than that by the natural dropping method.